3, 5-dichloro-2, 6-dimethoxybenzoates



United States Patent Dfiice 3,013,060 Patented Dec. 12, 196 1 3,013,060 3,5-DICHLORG-2,6-DIMETHOXYBENZOATES Sidney B. Richter, Chicago, Ill., assignor to Velsicol Chemical Corporation, Chicago, 111., a corporation of Illinois No Drawing. Filed Nov. 10, I958, Ser. No. 774,810 12 Claims. (Cl. 260-473) This invention relates .to new herbicidal compositions of matter. More specifically, this invention relates to the control of undesirable plant life with 2,6-dimethoxy-3,5- dichlorobenzoic acid, its anhydride, its amides, its esters, its alkali metal salts, or its amine salts. 2,6-dimethoxy- 3,5-dichlorobenzoic acid, which has the structure (JOOH HaO 0 CH3 will hereinafter be referred to as compound I. This chemical compound and its derivatives as cited above have marked activity as herbicides useful for the control of undesirable plant life.

Compound I can be obtained readily, for example, by the chlorination of 2,6-dimethoxybenzoic acid or by the further chlorination of 2,6-dimethoxy-3-chlorobenzoic acid. The chlorination can be effected with gaseous chlorims, and inert solvents or diluents such as chloroform or carbon tetrachloride can be used. Although the chlorinations proceed satisfactorily at room temperature, reaction temperatures up to the refiux temperatures of the solvents or diluents employed can be used. In order to prevent cleavage of the ether groups by any free hydrogen chloride which may form during the chlorination, a few percent of an acid scavenger such as calcium carbonate can be added to the reaction mixture. If 2,6-dimethoxybenzoic acid is used as the starting material, the chlorination is continued until slightly more than the amount of chlorine theoretically required for the introduction of two gram atoms of chlorine into the molecule of starting material has been taken up by the reaction mixture. If 2,6-dimethoxy-3-chlorobenzoic acid is used as the starting material, only slightly more than the amount of chlorine corresponding theoretically to one gram atom of chlorine per molecule of starting material need be taken up by the reaction mixture. The crude product can be isolated by distilling off the solvent or diluent. Although the compound I obtained in this matter is suitable for many herbicidal uses as such, the pure compound I can be obtained, for example, by fractional crystallization of the product from a suitable solvent.

The anhydride of compound I is prepared by the re- ,moval of one molecule of water from two molecules of compound I as the free acid. In practice, it is convenient to prepare the anhydride by the acylation of the free carboxylic acid by its acid halide in the presence of a strong acylating agent such as pyridine. Thus a mixture of dry pyridine and dry benzene are treated with 1 mole of the acid chloride of compound I. The slightly exothermic reaction proceeds with the formation of an intermediate pyridinium salt. One mole of compound I as the free acid is then added, the precipitate of pyridine hydrochloride is removed, and the anhydride of compound I is isolated by removal of the benzene.

The acid halide of compound I required in the above and other syntheses is prepared by the reaction of the free acid with a phosphorus trihalide in the conventional manner. Thus the treatment of compound I with phosphorus trichloride until the reaction ceases produces the acid chloride of compound I.

Compounds which are salts, esters, or amides of compound I can be prepared readily from the free acid. Thus treatment of the free acid with ammonium hydroxide gives a product which is the salt ammonium 2,6-dimethoxy-3,S-dichlorobenzoate. Similarly, an alkali metal salt of compound I can be made by the treatment of the free acid with bases, such as the hydroxides, of alkali metals. Treatment of the acid with sodium hydroxide thus gives the salt sodium 2,6-dimethoxy-3,S-dichlorobenzoate as the product, while the use of potassium hydroxide gives the salt potassium 2,6-dimethoxy-3,5-dichlorobenzoate.

Amine salts of compound I are prepared by the addition of the free acid to various amines. Typical amines which can be used to prepare such amine salts are dimethylamine, trimethylamine, triethylamine, diethanolamine, triethanolamine, isopropylamine, morpholine, and the like. The resulting products are, respectively, the dimethylamine, trimethylamine, triethylamine, diethanolamine, triethanolamine, isopropylamine, and morpholine salts of 2,6-dimethoxy-3,S-dichlorobenzoic acid.

Esters of compound I are prepared by the condensation of the acid with various alcohols. Thus the condensation of methyl alcohol with compound I gives the desired ester, methyl 2,6 dimethoxy 3,5 dichlorobenzoate. Other typical alcohols which can be used are propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl, and the like. The products are the corresponding alkyl esters of 2,6-dimethoxy-3,S-dichlorobenzoic acid. Although such complex esters as those prepared by the esterification of compound I with butoxyethanol, propylene glycol butyl ether, and the like are useful products in accordance with this invention, preferred esters are those in which the esterifying group is an unsubstituted alkyl group which contains from 1 to 10 carbon atoms. The condensation of the acid with the alcohol is carried out suitably in an inert solvent such as an aromatic hydrocarbon and in the presence of a few percent by Weight of an acid catalyst such as p-toluenesulfonic acid. The Water which forms during the esterification reaction can be removed continuously in many cases from the reaction mixture by distillation as it forms, and its volume can be measured to determine when theesterification is complete. The ester is then isolated by distillation of the inert solvent.

Amides of compound I can be prepared conveniently by the reaction of the acid halide of compound I with ammonia or various amines. The reaction can be carried out in an inert solvent such as ether or benzene. Preferably two moles of the amine are used for each mole of the acid halide employed, since the hydrogen halide released during the reaction is taken up by some of the free amine which remains. The simplest amide, 2,6-dimethoxy-3,S-dichlorobenzamide, can be prepared by the reaction of the acid chloride of compound I with arm monia,either as the free gas or as an aqueous solution. This amide can also be prepared by hydrolysis of the corresponding nitrile. Substituted amides are prepared by the reaction of the acid halide of compound I with amines such as any of the primary or secondary amines suggested above for the preparation of the amine salts of compound I. Thus, for example, the reaction of the'acid chloride of compound I with methylamine, butylamine, decylamine, or diethylamine gives the N-methyl-, N-buty1-, N-decyl-, or N,N-diethyl-2,6-dimethoxy-3,S-dichlorobenzamides, re-

spectively. While more complex amines such as the aromatic amines can be used as the amine reactant to give desirable products, which are specifically named as anilides, preferred amine reactants are alkylamines containing up to 10 carbon atoms.

For practical use as herbicides, the compounds of this invention are formulated with inert carriers to obtain proper concentrations and to facilitate handling. Forexample, these compounds can be formulated into dusts by combining them with such inert substances as talc or clays. The alkali metal salts of compound I are particularly suited to such dust formulations, and dusts containing from to 25 percent by weight of active compound are convenient for use in the field. The compounds of this invention, however, are preferably applied as sprays. These can be made as simple solutions by dissolving the compounds in organic solvents such as xylene, kerosene, or the methylated naphthalencs. The esters of compound I, which ordinarily are liquids at room temperature, are particularly suited to formulation by this method. The amine salts of compound I often shown good solubility in water and can be used directly as aqueous solutions.

The compounds of this invention can also be emulsified or suspended in water by the addition of emulsifiers and wetting agents. The formulations of these active herbicidal compounds are either applied directly to the plants to be controlled, or the soil in which the plants are growing can be treated. Substances such as other pesticides, stabilizers, activators, synergists, spreaders and adhesives can be added to the formulations if desired. There is no significant difference in effect from the amount of Water or organic solvent for diluting these herbicides, providing the same amount of chemical is distributed evenly over a given area. Such distribution can be obtained, for example, with low-pressure, low-volume sprays at the rate of about gallons of spray per acre.

In applying the herbicidal compounds, consideration must be given to the nature and stage of growth of the crop, the species of weeds present, the stage of growth of the weeds, environmental factors influencing the rate and vigor of the weed growth, weather conditions at the time of application and immediately following, and the dosage to be applied to a given area. Weeds are most susceptible when they are small and growing rapidly. Early application, therefore, results in better control with less chemical and increased yields because of the early destruction of the competing weeds. The larger and older the weeds the higher the concentration needed to kill them. Summer annuals such as lambs-quarters, pigweeds, cocklebur, and sunflower .should be sprayed when they are less than 4 inches high. Winter annuals such as various mustards, fanweed, yellow star-thistle, and wild radish are most easily killed while they are still in the rosette stage. Usually weeds growing rapidly under optimum conditions are relatively susceptible, whereas those growing under adverse conditions tend to be resistant to the herbicide sprays.

The effectiveness of the compounds of this invention in small quantities makes them economically sound for weed control on large areas, with a great saving in labor and cost, in addition to corresponding crop increases. These compounds are particularly valuable in weed control because they are harmful to many weeds but harmless or relatively harmless to some cultivated .crops. Minute quantities in contact with plant tissues may be absorbed and translocated to all parts of the plant, causing striking changes in the form and functions and often resulting in theirdeath. Theactual amount of compound to be used depends on a variety of factors but is influenced primarily by the species of undesirable plant to be controlled. Thus while fractions of a pound of actual-compound I or its equivalent of an ester, salt, amide, or the anhydride of compound I are often sufiicient for postemergence Weed control on an acre of corn, seed fiax, perennial grass seed crops,pastures or grazing areas (withoutlegumes), wheat,

and the like, the particular species of weeds encountered in evergreen and deciduous dorm ant nursery stock, nursery conifiers, waste areas, woody brush, and the like may require the use of one or more pounds of compound I or its derivatives per acre for good control. Dosage adjustgested can be made by changing the nozzle size, nozzle spacing, pressure, or traveling rate ofthe spray equipment.

'ments with the low-volume, low-pressureapplications sug- V The manner in which the herbicidal compounds of this invention can be prepared and utilized is illustrated in the following examples:

EXAMPLE 1 Preparation of 2,6-dimethoxy-3-chlorobenzoic acid EXAMPLE 2 Preparation of 2,6-dimethoxy-3,S-dichlorobenzdic acid (compound I 2,6 dimethoxy 3 chlorobenzoic acid (0.5 mole) is placed with one liter of chloroform and 2.5 g. of dry calcium carbonate in a 2-liter, round-bottomed flask fitted with a reflux condenser, mechanical stirrer, internal thermometer, and a gas inlet tube with a sparger tip. The mixture is stirred vigorously while chlorine gas is passed into the mixture. The gassing is continued until 10% more than the theoretical weight of chlorine calculated for the introduction of one gram atom of chlorine into the molecule of starting material has been taken upby the reaction mixture. The cooled reaction mixture is filtered, and the chloroform is then removed by distillation in vacuo to leave a residue containing the desired compound I, which can be isolated by fractional crystallization of the residue from a suitable solvent.

EXAMPLE 3 Preparation of the sodium salt of compound 1 EXAMPLE 4 Preparation of the ammonium salt of compound I Treatment of compound I (0.5 mole) in 500 cc. of methanol with 34 cc. of commercial concentrated ammonium hydroxide according to the method given in the previous example gives the desired ammonium salt of compound I.

EXAMPLE 5 Preparation of the dimethylamine salt of compound 1 Compound I (0.5 mole) is dissolved in 500 cc. of dry ether and treated with dimethylamine (22.5 g.; 0.5 mole). The solid which separates is filtered, washed twice with cc. portions of cold ether, filtered, pressed dry, and dried completely in a vacuum oven to give the desired dimethylamine salt of compound I.

. EXAMPLE 6 Preparation oj the diethunolamihe salt of compound I In the manner described in the previous example, compound 1 0.5 mole) is treated with diethanolamine 52.5

g.; 0.5 mole) in 500 cc. of dry ether. The product which is isolated is the diethanolamine salt of compound 1.

EXAMPLE 7 Preparation of the morpholine salt ofcompound 1 Compound I (0.5 mole) ethyl alcohol (23 g.; 0.5 mole), and 3.0 g. of p-toluenesulfonic acid are dissolved in 500 ml. of benzene, and the solution is placed in a 1-liter, round-bottomed flask fitted with a reflux condenser and a calibrated DeanStark tube. The solution is heated at reflux temperature until 9 cc. of water have been collected in the Dean-Stark tube. The cooled reaction mixture is then extracted twice with 50-cc. portions of 10% sodium carbonate solution, and filtered. The benzene is distilled off in vacuo on the steam bath, and the residue is then distilled in vacuo to give the desired ethyl ester of compound I.

EXAMPLE 9 Preparation of the decyl ester of compound I In the manner and apparatus described in the previous example, compound I (0.5 mole) and normal primary decyl alcohol (79 g.; 0.5 mole) are refluxed in 500 ml. of benzene in the presence of 3.0 g. of p-toluenesulfonic acid until 9 cc. of water have been distilled from the reaction mixture. Work-up of the reaction mixture as described in the previous example gives the desired decyl ester of compound I.

EXAMPLE 10 Preparation of the n-butyl ester of compound I The reaction of compound I (0.5 mole) and n-butyl alcohol (37 g.; 0.5 mole) by the method described above for the preparation of the ethyl ester is used to prepare the n-butyl ester of compound 1.

EXAMPLE 11 Preparation of the acid chloride of compound I Compound I (1 mole) is placed with 500 cc. of dry benzene in a 2-liter, 3-necked, round-bottomed flask fitted with a mechanical stirrer, reflux condenser (calcium chloride tube), and dropping funnel. Phosphorus trichloride (123 g.; 0.9 mole) is added slowly dropwise with vigorous stirring while the reaction flask is cooled with cold water if necessary to control the reaction. When all the PCl has been added and the evolution of hydrogen chloride has ceased, the reaction mixture is then transferred to distillation apparatus, and the solvent is distilled otf. The residue is then distilled in vacuo to give the desired acid chloride of compound I.

EXAMPLE 12 Preparation of the amide of compound 1 One mole of the acid chloride of compound I is placed with 500 cc. of dry benzene in a l-liter, 3-necked flask fitted with a reflux condenser, mechanical stirrer, and a gas inlet tube having a sparger tip. The mixture is stirred while dry ammonia gas is passed into the mixture for several hours. When the ammonia gas is no longer taken up, the precipitated salt is filtered olf and extracted twice with 100 ml. portions of ether. The ether extracts and benzene filtrate are dried over magnesium sulfate and filtered, and the solvents are distilled off to give the desired amide of compound I.

EXAMPLE 13 Preparation of the N-n-aecylamide of compound I One mole of the acid chloride of compound I and 500 ml. of dry benzene are placed in a 2-liter, S-necked, round-bottomed flask fitted with a mechanical stirrer, reflux condenser, internal thermometer, and dropping funnel. n-Decylamine (314 g.; 2.0 moles) in 250 ml. benzene is added dropwise with vigorous stirring. When all the amine has been added, the reaction mixture is refluxed for 2 hours and cooled, afiter which the precipitated EXAMPLE 14 Preparation of the N,N-diethylamide of compound I One mole of the acid chloride of compound I is treated with diethylamine (146 g.-; 2.0 moles) in the manner and apparatus described in the previous example to give the N,N-diethylamide of compound I.

EXAMPLE 15 Preparation of the anhydriae of compound I Dry pyridine (158 g.; 2.0 moles) and 1 liter of dry benzene are placed in a 2-liter, 3-necked, round-bottomed flask fitted with a dropping funnel, mechanical stirrer, reflux condenser, and internal thermometer. One mole of the acid chloride of compound I, which is prepared as described in a previous example, is added rapidly with stirring to the reaction mixture. Compound I (1 mole) is then added in portions over a period of about 10 minutes with rapid stirring. The pyridine hydrochloride which precipitates is filtered ofl, and the benzene is distilled from the filtrate in vacuo. The residue contains the desired anhydride of compound I, which can be purified by crystallization from a suitable solvent.

EXAMPLE 16 Preparation of an emulsifiable' concentrate of compound I The following concentrate is prepared by mixing the ingredients intimately in the given percentage proportions by weight:

Percent Compound I 25 Antarox A-400 40 Methanol 35 Antarox A-400 is the trade name under which a nonionic detergent of the aromatic polyethylene glycol ether type is sold. The above concentrate is diluted with water to the desired concentration for use.

EXAMPLE 17 Preparation of an emulsifiable concentrate of the n-butyl ester of compound I The following ingredients are mixed thoroughlyv in the given percentage proportions by weight:

Triton X-lOO is the trade name under which an emulsifier of the alkyl aryl polyether alcohol type is sold. The above concentrate is diluted with water to the desired concentration for use.

EXAMPLE 18 Preparation of a dust from the sodium salt of compound I The sodium salt of compound I (10% by weight) and talc by weight) are combined and ground to the desired particle size in a mechanical grinder-blender.

The herbicidal activity of chemical compounds is often demonstrated by the ability of the chemicals to kill or arrest the growth of tomato plants. The tomato plant is readily grown and maintained under uniform conditions for experimental purposes in greenhouses, and its response to chemicals is very similar to that observed for a wide variety of economically important species of undesirable plant life in the field.

The herbicidal activity of the compounds of this invention, for example, can be demonstrated in greenhouse experiments on young potted tomato plants (Bonny Best variety). The compounds are formulated into 10 percent ive'tt'able powders and are dispersed in water at a concentration of 2,000 parts per million actual chemical. Ten milliliters of an aliquot portion of the dispersion is added to the soil surface of the tomato plants, approximately to 7 inches tall. In order to avoid undue concentration or accumulation of the chemical in any given area, 5 holes the siie of a pencil and about 1. inch deep are punched in the-soil surfacearound the shoot, and the 10 milliliter application is divided equally among the 5 holes. Three plants are used for each application. Thetreated plants are held under greenhouse conditions for 7 days, provided with subterranean watering, and observed for response to treatment. The results indicate a high order of herbicidal toxicity of the compounds of this invention.

I claim as my invention:

'1. A compound selected from the group consisting of 2,6-dimethoxy-3,S-dichlorobenzoic acid, its anhydride, its alkali metal salts, its ammonium salt, its morpholine salt, its al-kyl amine salts in which the amine component is an unsubstituted alkyl amine of up to six carbon atoms, its al-kanol amine salts in which the amine component is an unsubstituted alkanol amine of up to six carbon atoms, its butoxyet-hanol ester, its esters in which the esterifying group is an unsubstituted alkyl group of from one to ten carbon atoms, its unsubstituted amide, and its alkyl amides in which the amine component is an unsubstituted alkyl amine of up to ten carbon atoms.

2. An alkali metal salt of 2,6-dimethoxy-3,S-dichlorobenzoic acid.

3. An alkyl amine salt of 2,6-dimethoxy-3,S-dichlorobenzoic acid wherein the amine component is an unsubstituted alkyl amine of up to six carbon atoms.

4. An ester of 2,6-dimethoxy-3,S-dichlorobenzoic acid in which the esterifying group is an unsubstituted alkyl group of from one to ten carbon atoms.

5. An alkyl amide of 2,6-dimethoXy-3,5-dichlorobenzoic acid wherein the amine component is an unsubstituted alkyi amine of up to ten carbon atoms.

6. An alkanol amine salt of 2,6-dimethoXy-3,5-dichlorobenzoic acid wherein the amine component is an unsubstituted alkanol amine of up to six carbon atoms.

7. The dimethylamine salt of 2,6-dimethoxy-3,5-dichlorobenzoic acid.

8. 2,6-dimethoxy-3,5 dichlorobenzoic acid.

9. Sodium 2,6-dimet hoxy-3,5-dich1orobenzoate.

10. The diethanolamine salt of 2,6dimethoXy-3,5-dichlorobenzoic acid.

11. n Butyl 2,6-dimethoxy-3,5-dichlorobenzoate.

12. Bis(2,6 dimethoxy 3,5 dichlorobenzoic) anhydride.

- ReferencesCited in the file'of this patent UNITED STATES PATENTS OTHER REFERENCES Hirwe et al.: Proc. Indian Acad. Sci, 8A, 208-213 (1938).

Cartwright et a1.: (1952).

J. Chem. Soc. (London), 3501 

1. A COMPOUND SELECTED FROM THE GROUP CONSISTING OF 2,6-DIMETHOXY-3,5-DICHLOROBENZOIC ACID, ITS ANHYDRIDE, ITS 2,6-DIMETHOXY-3,5-DICHLOROBENZOIC ACID, ITS ANHYDRIDE, ITS ITS ALKYL AMINE SALTS IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKYL AMINE OF UP TO SIX CARBON ATOMS, ITS ALKANOL AMINE SALTS IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKANOL AMINE OF U P TO SIC CARBON ATOMS, ITS BUTOXYETHANOL ESTER, ITS ESTES IN WHICH THE ESTERIFYING GROUP IS AN UNSUBSTITUTED ALKYL GROUP OF FROM ONE TO TEN CARBON ATOMS, ITS UNSUBSTITUTED ALKYL GROUP OF FROM ONE TO AMIDES IN WHICH THE AMINE COMPONENT IS AN UNSUBSTITUTED ALKYL AMINE OF UP TO TEN CARBON ATOMS.
 4. AN ESTER OF 2,6-DIMETHOXY-3,5-DICHLOROBENZOIC ACID IN WHICH THE ESTERIFYING GROUP IS AN UNSUBSTITUTED ALKYL GROUP OF FROM ONE TO TEN CARBON ATOMS. 